This invention relates generally to roller thrust bearings. More particularly, the invention provides a new and improved thin roller thrust bearing assembly for use in an automotive automatic transmission or the like.
In an automatic transmission or similar device, relatively thin, highly loaded thrust bearings are required between the working members of the device. In the conventional automatic transmission, an impeller, one or more turbines, and a stator form a torus shaped container containing a fluid which transmits torque from the impeller to the turbines and to the drive shaft of the vehicle when the impeller is rotated by the engine. In such a device, the rotating, working members rotate at relatively high relative velocities with centrifugal force and hydrostatic pressure creating unavoidably heavy thrust between relatively rotating members. However, at the same time, because of space limitation, the thrust bearings must be relatively thin. In the gear box the helical gears of the planetary gear system of the conventional automatic transmission create the same operating conditions and present another application for the bearing of the present invention.
Typically, in the prior art, these thrust bearings comprise first and second annular races with a plurality of rolling elements and an annular roller retaining cage disposed therebetween. Since a relatively large number of these bearings normally are necessary in an automotive transmission assembly, recent development in these types of bearings has been directed to reducing bearing cost, rather than improving bearing performance. For example, these bearings are now assembled from stamped or drawn metal parts whenever possible. Typically, the first and second annular races are flat, stamped, or drawn members, including an axially projecting flange on the inner or outer diameter of the race. The annular cage is comprised of first and second ring-shaped, stamped or drawn cage members which interlock, retaining a plurality of rolling elements therebetween.
In these prior art thrust bearing assemblies, it has always been considered necessary to additionally provide means for mechanically retaining or binding together the assembly. In some cases this comprised an outer banding cup encompassing first and second flat annular races. However, the banding cup in this prior art bearing configuration, besides requiring an extra part in the forming operation, interfered with the flow of lubricant to the assembly. Alternatively, the raceways were provided with complimentary L-shapes when viewed in cross section, having projections on the edges of the flanges of each raceway. The complimentary L-shaped raceways having flanges and projections were forced over the cage with the cage and the projections forming an interference fit preventing separation of the races.
Problems with this latter type of assembly employing flanges and projections to mechanically secure the bearing assembly include accidental separation of the assembly and manufacturing problems associated with forming the projections on a stamped or drawn metal part. Tooling limitations dictate that the projections be formed or stamped with working members approaching the race from the axial direction. Thus, the flanges must be formed on the race in a stamping or drawing process that takes place after the formation of the projections. However, the stamping die must then be relieved to allow for the passage of the projections. Because of this, the die, which creates the flanges, produces flanges having a non-uniform radius and distorted raceways. Solutions to this problem have included the steps of coining the roller pathway to remove distortions and providing a relief hole in the raceway immediately adjacent the projections to reduce distortion during the drawing process. These steps, particularly the coining step, have proved expensive and still have not completely solved the problem of providing a stamped metal raceway having an undistorted roller pathway.
Various methods have been employed over the years to retain radial bearing assemblies. These methods have included grease retention of radial bearing assembly components. However, relatively thin roller thrust bearings of the type herein described for use in an automotive automatic transmission, have never been grease retained. These bearings have always been mechanically retained in the axial direction at some expense and difficulty.